An extraction process for which the invention may be used involves the contacting of two liquid phases wherein the liquids are substantially immiscible and of different densities such as an aqueous-organic extraction process. However, the invention may also be used in an extraction process involving two miscible liquids which have specific gravity differences sufficient to result in two separate phases. Prior devices for effecting this kind of liquid-liquid extraction comprise a number of mixing and settling tanks which alternate in series with the liquids flowing countercurrently to one another. These prior devices utilize strong agitation in the mixing stages which often has resulted in the formation of emulsions or three phase systems which causes a reduction in the efficiency of such processes by prolonging the separation times. The prior devices also often require pumping means for transferring the liquids from one stage to another. Such pumping means may comprise complex arrangements of pipes, valves and pumps which add significantly to the cost while reducing the reliability of the device.
Prior devices generally have employed means for thoroughly agitating the liquids in the mixing stages in order to achieve maximum extraction efficiency at each stage and thereby minimizing the number of stages needed to effect the desired extraction. In addition to the disadvantages aforementioned relating to such prior devices, this thorough agitation is energy intensive and with the present high cost of energy detracts from the cost effectiveness thereof.